1. Field of the Invention
This invention relates to methods and devices for treating congestive heart failure by deploying and tensioning a cardiac assist device about the heart. More specifically, this invention relates to methods and devices for deploying, positioning and tensioning a congestive heart failure passive restraint device adjacent the pericardium of the heart in a minimally invasive manner.
2. Prior Art
Heart failure syndrome is a highly debilitating and degenerative disorder resulting from damage to the heart muscle. The damage to the heart muscle may be caused by a number of conditions, including coronary artery disease, long standing hypertension, compromised heart valve(s) function, infection and diabetes.
Heart failure typically occurs when a weakened heart cannot pump an adequate amount of blood to meet the demands of the body's other organs and tissues. The defining characteristic in the progression of heart failure is that there is eventually a reduction of the heart's ability to meet the metabolic needs of the body.
Whatever the cause or source of damage, the heart's ability to pump adequate amounts of blood to support the body's needs is diminished, and the progressive deterioration of cardiac physiology and function begins. The inadequate supply of oxygen-rich blood often causes people with heart failure to experience shortness of breath and fatigue during even routine daily activities. As the condition progresses, the contraction rate of the heart increases in response to decreasing cardiac output. As a result, the chambers of the heart, particularly the ventricles of the heart, become increasingly enlarged as the heart tries to compensate for the inefficiencies. FIGS. 1a-1c show representative stages of progressive deterioration of a heart, wherein FIG. 1a shows a normal heart 10 with appropriately sized atrial chambers 1 and 2, and appropriately sized ventricular chambers 3 and 4, FIG. 1b shows slightly enlarged ventricular chambers 3 and 4, and FIG. 1c shows increasingly enlarged ventricular chambers 3 and 4. Ultimately, a complex process of damaging structural and functional changes to the heart results.
The disease of heart failure is common, lethal, and expensive to treat. An estimated 5.1 million Americans have heart failure with approximately 500,000 new cases diagnosed each year. In 1999, an estimated $20.3 billion in directs costs were spent for the care of heart failure patients. Heart failure is also the most common cause of hospitalization for patients 65 years and older in the United States. The mortality rate is 50% at five years for patients diagnosed with heart failure, and to date, there are limited treatment alternatives available.
Certain cardiac disease treatment devices have been proposed to help alleviate the disease of heart failure. For example, U.S. Pat. No. 6,425,856 provides a cardiac constraint device comprised of a jacket made of biologically compatible material. The jacket is configured to surround a valvular annulus of the heart and at least the ventricular lower extremities of the heart. FIG. 1d illustrates how the jacket 20 may be positioned around the heart 10 to improve cardiac function. The jacket works on a passive, mechanical level to reduce periodic myocardial over-stretch and wall stress, interrupts the angle of continual further expansion of the ventricular walls, and serves as a constant “reminder” to the heart of how it should perform. The jacket thus encourages down-regulation of increased local neurohormonal activity, and reduction or elimination of cardiomyocyte maladaptive gene expression.
These actions may halt the progressive deterioration of the heart and may stimulate reverse remodeling of the heart. Mechanisms responsible for remodeling of the heart are not singular and vary from patient to patient. For many patients, remodeling can occur through multiple mechanisms. Sometimes the individual mechanisms act synergistically to achieve an effect that exceeds the simple additive effect of non-interacting mechanisms.
Once positioned as desired around the heart, the jacket 20 is sutured to the heart. The deployment of a jacket is a method for deploying a material or structure that interrupts the cycle of heart failure. The minimum expectation would be to slow the progression of the disease; the preferred expectation would be the reduction of the disease (i.e., remodeling). The effect of the jacket can be on muscle cells, connective tissues, vascular tissues and enervation tissues. Ideal positioning of the jacket around the heart has proved problematic however, particularly where endoscopic tools and techniques are used. Other current procedures deploy the mesh through traditional open sternotomy procedures, which are very invasive.
An alternative procedure for surrounding a heart with a cardiac assist device proposes endoscopically placing a mesh underneath the heart and then pulling corners of the mesh sheet up and around the heart, as disclosed in co-pending U.S. patent application Ser. No. 10/881,510, filed Jun. 30, 2004, of common assignment herewith. Each corner of the mesh sheet is provided with suture tethers that are pulled in a designated sequence in order to wrap the mesh sheet around the heart.
Anatomically, as shown in FIG. 2, the pericardial sack 200 covers the heart 210 and connects to the veins 220 superiorly and to the diaphragm 230 inferiorly. It is possible to access the pericardial sack under the sternum 240, by dissecting just under the sternum. Conventionally, such access has been used to introduce drugs, growth factors, stem cells, etc., but not to help alleviate congestive heart failure or the conditions leading thereto.
Therefore, a need exists for methods and devices that deploy, position and tension a cardiac assist device around the pericardium of the heart in a relatively quick and minimally invasive manner.